1. Field of the Invention
The present invention relates to image processing, and more particularly, to a method and apparatus for eliminating chromatic aberration.
2. Description of the Related Art
Chromatic Aberration (CA) is an aberration caused by a difference in refractive index according to different wavelengths of light. In an ideal lens, white light that is incident to the lens must be focused on one point of an image formed on a plane after the white light passes through the lens. However, in an actual lens, light having a relatively short wavelength is refracted more than light having a relatively long wavelength so that focus varies according to the wavelengths of light due to the difference in refractive index according to the different wavelengths. In other words, focus varies according to colors of light. A color image is formed of colors such as red (R), green (G), and blue (B). As described above, light of different colors focuses on different spots due to an effect of the lens and thus, false colors are generated in the image. This is known as chromatic aberration.
Chromatic aberration may be mainly classified into longitudinal chromatic aberration and lateral chromatic aberration. Longitudinal chromatic aberration is caused due to a focus difference on an optical axis, and lateral chromatic aberration is caused due to a difference in magnification according to color. Longitudinal chromatic aberration and lateral chromatic aberration are not generated separately and instead, are generated together.
Chromatic aberration may be observed in most optical devices using a lens. In manufacturing of the lens used in optical devices, various lenses are combined to correct the chromatic aberration. However, even if the lenses are combined, chromatic aberration cannot be completely eliminated. Also, in most cameras installed in mobile phones and typical compact cameras, inexpensive lenses are used and thus, the chromatic aberration may be more conspicuous. Moreover, although resolutions of cameras installed in mobile phones and digital cameras are rapidly increasing, lens quality does not proportionally increase due to cost and size of the lenses. That is, chromatic aberration is generated mostly in cameras and manufacturers of the cameras try to reduce the chromatic aberration.
A conventional method of eliminating chromatic aberration comprises matching sizes of three channels, R, G, and B, in order to compensate the chromatic aberration generated due to lateral chromatic aberration. In order to match the sizes of the three channels, an interpolation process is required, in which displacement in each channel is predicted, a proportion of a size of an image is obtained through predicted information, and the sizes of two channels are matched to the size of the remaining single channel. Here, shifts and scaling parameters of the R, G, and B channels are calculated according to a registration algorithm, the registration algorithm using a black and white image having a specific pattern. That is, corner points having the specific pattern are extracted and matched for each channel and then, scaling information is identified using the corner points.
In the conventional method, lateral chromatic aberration can be efficiently eliminated as the sizes of the images are matched by predicting displacement of the channels. However, if the conventional method is used, registration information must be previously predicted by each lens through the specific pattern and then, the chromatic aberration is eliminated using the parameters (that is, registration information must be known for all lenses in advance), and extracting the parameters and eliminating the chromatic aberration are separated since the registration algorithm must be performed independently by using the image having the specific pattern. In addition, the conventional method is not effective in DSLR cameras in which lenses are changed. Furthermore, DSLR cameras have limitations in correcting chromatic aberration caused by longitudinal chromatic aberration and lateral chromatic aberration together since longitudinal chromatic aberration is not considered in DSLR cameras.